The ballast supporting a railroad track must be compacted from time-to-time to maintain track integrity. Accordingly, a variety of tamping devices have been developed over the years. In general, a tamping device utilizes one or two pairs of tamping units having tool blades that are inserted into the ballast where they are vibrated in some fashion to compact the ballast. Each pair of tamping units has first and second tool blades inserted on either side of a track's railroad tie adjacent the track's rail. Once inserted into the ballast, a vibration mechanism causes the tool blades to vibrate.
Prior art tamping devices fall into two general categories. The first category vibrates the tool blades such that they oscillate perpendicular to the track's tie. The second category oscillates each tool blade through a small angle with respect to a vertical axis of the tool blade's tamping unit. The tamping operation of each category will be explained further below with the aid of FIGS. 1–3.
The above-noted first category of tamping devices will be described with the aid of FIGS. 1 and 2 where a railroad track's tie 10 is shown supporting one of the track's rails 12 with the area beneath and around tie 10 and rail 12 comprising ballast 14 as is well known in the art. In this example, two pairs of tamping units are used with only the tool blades thereof (that interact with ballast 14) being illustrated. Specifically, a first tamping unit pair has tool blades 20 and 22, and a second tamping unit pair has tool blades 30 and 32 positioned/inserted into ballast 14 with tool blades 20/22 positioned on opposing sides of tie 10 along one side of rail 12, and tool blades 30/32 positioned on opposing sides of tie 10 along the other side of rail 12. A motor driven vibration apparatus (not shown for clarity of illustration) is coupled to tool blades 20/22 and 30/32 to vibrate/oscillate the blades back and forth in a direction that is perpendicular to tie 10 as indicated by motion arrows 21, 23, 31 and 33. The vibratory motion can occur in a straight line or single plane fashion, or can occur along pendulum-like arcs (e.g., arcs 21A and 23A for tool blades 20 and 22, respectively) as shown in the side view of FIG. 2. An example of such a tamping device is disclosed by Pasquini in U.S. Pat. No. 4,218,978.
The above-noted second category of tamping devices will be described with the aid of FIG. 3. In this example, each of tool blade pairs 20/22 and 30/32 are again positioned/inserted into ballast 14 as in the previously-described example. The corresponding vertical axis of each tamping unit (not shown) is indicated at 20A, 22A, 30A and 32A, respectively. A motor driven vibration apparatus (once again not shown for clarity of illustration) is coupled to the tool blades to vibrate/oscillate each tool blade through a small angle α (e.g., on the order of approximately 2.5°) about each tamping unit's respective vertical axis as indicated by motion arrows 25, 27, 35 and 37. An example of such a tamping device is disclosed by Morgan et al. in U.S. Pat. No. 6,386,114.
The most critical region in a railroad track's ballast lies beneath the intersection of a tie and rail. However, none of the prior art tamping tools and/or vibration methodologies are very effective at applying compacting forces to the critical tie-rail intersection region of a railroad track's ballast.